Bees exhibit diverse nesting strategies, adapting to various environments. While many species prefer underground burrows or sheltered spots, a significant number utilize trees as their primary nesting sites. These arboreal habitats offer specific advantages, attracting various bee species. Understanding which bees favor trees and why provides insight into their ecological needs and behaviors.
Common Tree-Nesting Bee Species
Honey bees, specifically the Western honey bee (Apis mellifera), frequently establish colonies within hollow tree cavities. These social bees construct beeswax combs that can house tens of thousands of individuals. Wild honey bee populations in temperate regions rely on these natural tree hollows for survival. Their presence in trees is the result of a swarm seeking a new, sheltered home.
Bumblebees (Bombus species) are another group that may use trees for nesting. While many nest underground in abandoned rodent burrows, some species occupy hollow logs, tree roots, or disused bird nests in trees. Their nests are smaller than honey bee colonies, containing hundreds rather than thousands of bees. Tree bumble bees, for example, nest in tree cavities or bird boxes.
Solitary bees include tree-nesting species. Leafcutter bees (Megachile species) and mason bees (Osmia species) are cavity-nesting insects that do not excavate their own tunnels. Instead, they use existing holes and crevices in dead wood, hollow plant stems, or natural cracks in tree bark. These bees provision individual cells within these tunnels with pollen and nectar for their offspring. Carpenter bees (Xylocopa species), however, bore into dead timber or soft wood to create their nests.
Preferred Tree Nesting Sites
Honey bees, for example, favor hollow trunks or large branches, preferring cavities around 40 liters, though they use spaces from 20 to 100 liters. They seek entrance holes at least 3 meters (about 9 feet) above the ground. These cavities result from fungal decay or natural damage within live trees.
Bumblebees use cavities in tree roots, hollow logs, or abandoned bird nests nestled in branches. These sites provide a secure, pre-existing space for their smaller colonies. Solitary bees like leafcutters and mason bees depend on natural tunnels created by wood-boring insects or existing cracks in dead wood. Carpenter bees, which bore their own tunnels, target unpainted, dead wood like logs, stumps, or structural timbers.
Why Bees Choose Trees for Nests
Trees offer many benefits, making them appealing nesting sites for various bee species. The enclosed spaces within tree cavities provide protection from predators like birds and mammals that might otherwise raid exposed nests. The woody structure of trees also offers insulation, shielding bee colonies from extreme temperatures, whether it is the heat of summer or the cold of winter. This thermal stability is important for the survival and development of bee brood.
The inherent stability of a tree provides a secure foundation for a nest, reducing the risk of disturbance from wind or other environmental factors. Trees themselves can be a direct source of food for bees, providing abundant nectar and pollen from their blossoms. Honey bees also collect tree resin to produce propolis, a sticky substance used to seal gaps in their nests and provide antimicrobial protection against pathogens. This combination of shelter, stability, and proximity to resources makes trees highly suitable for bee reproduction and survival.
Distinguishing Bees from Look-Alikes in Trees
Tree-nesting bees are often confused with other insects like wasps or hornets, which may also occupy tree cavities. Bees generally possess more robust, rounded, and hairy bodies, which help them collect pollen. Their coloration often includes muted yellows, oranges, and browns, with less distinct banding compared to many wasps. Wasps, conversely, have smoother, more slender bodies with a distinct narrow waist and feature brighter, more contrasting yellow and black stripes.
Observing nest structure can also help in identification. Honey bees build their nests from wax, forming hexagonal comb structures inside a cavity. Wasps construct papery nests from chewed wood fibers mixed with saliva, which can appear as spherical or tiered structures. Bumblebee nests, while sometimes found in trees, consist of more haphazard wax cells and are lined with insulating materials like leaves or fur. Behavioral cues are also useful; bees are less aggressive and sting only when provoked or defending their nest, whereas some wasps are more defensive and sting multiple times.